In the case of a conventional novolak-naphthoquinonediazide resist, a method of using a high-molecular weight alkali soluble resin (for example, novolak resin) has commonly been employed so as to prepare a resist composition having high heat resistance. Also, a method of using a low-molecular weight resin has been employed so as to achieve high sensitivity.
However, it is difficult to reconcile sensitivity and heat resistance. When using the high-molecular weight resin, sensitivity tends to deteriorate and it was difficult to apply the resulting composition to a resist for TFT (thin film transistor) to which high sensitivity is required.
In the fields of a thick-film resist having a thickness of about 1.5 to 7.0 μm and system LCD (liquid crystal display) using low-temperature polysilicone as a substrate, heat resistance is severely required in the implantation step, and thus there is required a resist material which has excellent heat resistance without deteriorating sensitivity (rather high sensitivity).
On the other hand, there is proposed a chemical amplification type positive photoresist composition comprising an alkali soluble resin having a hydroxyl group in the side chain of a novolak resin, a specific crosslinking agent and a photo acid generator (PAG) (see, for example, Patent Documents 1 and 2).
Since this chemical amplification type positive photoresist composition is a resist which is lower in price than a conventional i-ray novolak resist and also has high heat resistance, high sensitivity and high resolution, its application to the fields of a thick-film resist (for example, 1.5 to 7.0 μm) in which high heat resistance and high sensitivity are required, and system LCD can be anticipated.    (Patent Document 1) Japanese Patent Application, First Publication No. Hei 6-148889    (Patent Document 2) Japanese Patent Application, First Publication No. Hei 6-230574
Recently, integration degree of semiconductor devices has increased more and more.
Various proposals have hitherto been made on a chemical amplification type resist which contributes to an improvement in integration degree of semiconductor devices.
In the following Patent Document 3, there is described a two-component resist comprising a base material resin wherein hydrogen of hydroxyl groups of polyhydroxystyrene having high transparency to KrF excimer laser beam is substituted with an acid dissociable alkali dissolution inhibiting group, for example, tertiary alkyloxycarbonyl group such as t-boc (tert-butoxycarbonyl) group or acetal group such as 1-ethoxyethyl group, and a photo acid generator as a main component.
A summary of principle of resist pattern formation in the resist proposed in Patent Document 3 is as follows. That is, since the base material resin has an alkali dissolution inhibiting group such as a t-boc group, alkali solubility is inferior to polyhydroxystyrene having no t-boc group. When such a resin is mixed with a photo acid generator and the mixture is selectively exposed, the t-boc group is dissociated by an action of an acid generated from a photo acid generator at the exposed area to produce polyhydroxystyrene, and thus the resin becomes alkali soluble.    (Patent Document 3) Japanese Patent Application, First Publication No. Hei 4-211258    (Patent Document 4) Japanese Patent Application, First Publication No. Hei 10-268508    (Patent Document 5) Japanese Patent Application, First Publication No. 2003-167357